1. Field of the Invention
The present invention is concerned with equipment for investment casting, and more particularly with apparatus for manufacturing easily fusible patterns. The invention is readily adaptable for application in various fields of engineering to enable automatic performance in the process of manufacturing easily fusible patterns for use in the production of precision-investment castings.
This invention can be advantageously utilized in foundry shops dealing with investment casting where quantity production of high-quality patterns is required.
2. Description of the Prior Art
It is modern practice to manufacture easily fusible patterns for metal castings from wax-type patterns materials.
The patterns are made by pressing-in said materials into a pressure casting die either in liquid state or by preliminarily transforming these materials into pasty state by injecting therein 15 to 20 percent of air.
In the process of injection of this liquid wax-like material into a pressure casting die, the latter should be kept under pressure until complete cooling of the pattern so as to prevent the formation of shrinkage cavities on the pattern surface. This, however, impairs the production efficiency of pattern making apparatus.
In addition, the resultant ceramic shell mould is subjected to considerable strains in the process of the pattern fusion due to appreciable thermal expansion of the pattern material. When thus effected by overdue strains, the mould tends to form cracks which may even cause its destruction, necessitating therefore higher consumption of additional materials and impairing quality of finished castings.
To make up for the pressure of the expanding pattern acting on the mould, the patterns are melted in steam autoclave plants under pressure of 5 to 6 atm. This, however, requires expensive and cumbersome equipment.
When making patterns by injection of pattern material into a pressure casting die, the air contained therein is compressed. Upon withdrawal of the pattern from the pressure casting die the air, tending to expand, causes either deformation or destruction of the pattern. To prevent this undesirable effect, it is necessary to increase the pattern hold-down time in the pressure casting die, which entails lower rates of production.
Moreover, the difficulty to maintain a constant amount of air in the pattern material, which air serves to adjust pressure difference in the mould, may result in the formation of cracks in the latter.
There are known in the art apparatus for manufacturing easily fisible patterns (cf. USSR Inventor's Certificate No. 337,184, cl. 22 7/02).
The apparatus of the Inventor's Certificate referred to above comprises a bed with a frame rigidly secured thereupon and carrying a pressure casting die composed of two parts, one of which is fixed on the frame and the other one is mounted for reciprocated movement in the horizontal, an injection means, a means for purging the pressure casting die inlet channel, a water tank, a heated receptacle for a pattern material, a pipeline system for delivery of pattern material to the injection means, and a common control system incorporating electric and pneumatic means adapted to enable automatic performance of the production process and re-cycling.
The injection means is formed of a heated body with a chamber for pattern material, intermittently communicating with the heated receptacle and with the pressure casting die cavity through horizontal and vertical channels of the intermediate means, said injection means also comprising an air cylinder with a hollow piston rigidly connected through its rod with the chamber and an injection mechanism arranged in the hollow rod and in the chamber.
The means for purging the inlet channel of the pressure casting die is provided with a needle fitted so as to be introduced into the channel of the pressure casting die through the horizontal channel of the intermediate means.
With the aforedescribed apparatus it is impossible to enhance the production efficiency, and the produced patterns fail to insure the production of high-quality moulds free from defects by reason of three-stage injection operation during which the pattern material undergoes injection accompanied by steadily mounting pressure in the cavity of the pressure casting die.
The first stage of the injection operation is effected at the expense of pressure required for forced supply of the pattern material to the chamber of the injection means.
The second stage of injection is carried out by the principal injection mechanism, and, finally, the third stage is performed by the needle of the means for cleaning the inlet channel of the pressure casting die, actuated on completion of the injection operation. As the needle advances into said channel, it pushes forward a batch of pattern material disposed in the gate channels of the pressure casting die, thereby increasing pressure in the latter.
It is therefore an object of the present invention to obviate the above disadvantages.
The primary object of the invention is to improve quality of the patterns being produced and enhance production efficiency of an apparatus.
Another object of the invention is to provide an apparatus for manufacturing fusible patterns wherein the supply of pattern material to a pressure casting die will be effected so as to preclude steadily mounting pressure of the pattern material in the pressure casting die.
Still another object of the invention is to provide an apparatus for manufacturing fusible patterns, which will enable the production of patterns having distinct imprint of the pressure casting die cavity.
Yet another object of the invention is to step up the process of cooling the produced patterns as well as to diminish thermal expansion thereof caused by heating during melting process.